That is totally personal, but there are fringe questions easily spotable. Example: You ask about this piece of Egyptian mythology, which appear to be written during Roman time. Thus false on Egyptian, false on Greekn true on Roman. So off-topic for Egyptian, off-topic for Greeks, on-topic for Romans. Still validated.
Regarding Rick Riordan, or any new author, there are a couple of ways to see the things:
- Any discussion on the books (quality, quality of writing, coherency, etc) doesn't pertain here.
- Answering a question with: In Rick Riordan's universe, things are like this, is perfectly valid (as long as the fact this is in Rick Riordan is very clearly mentioned)
- Any questions examining the sources/original stories are obviously quite welcome
My point is: Rick Riordan (which I have not read at all) is still a significant modern author; and lots of people can be introduced to standard myths by him! No one should reject that. Same with titles like God of War (the video game), or a character as Wonder Woman. Myths are used around them. And their impact on the modern culture is evident. Example: A couple of people around me got their first proper introduction to Baldr via the Baldur appearing in God of War. Quite popular questions I received is about the hieroglyphic writing in Assassin's creed origin or the runes in God of war.
You can have a better sight on that thinking about movies as Gods of Egypt or King Arthur. Their impact on modern culture is inexistant, still questions about the skin color of Horus, his golden blood, the fight between Horus and Seth are totally pertaining here.
Mythology and folklore is about what the soil of culture around believes. Rick Riordan's universe is definitely something we should not throw away too easily, due to its tremendous impact, especially on young people, as long as we keep concentrating on what is mythology and folklore. And seeing the huge difference between Rick Riordan and God of Egypt. Or as pointed by Semaphore The Once and future King and The Kid who would be King.
For what i am concerned, as long as we do not start a war on the "quality of writing" or who's is the strongest, or supposition on the universe, those books, movies, games are part of this site.
Beside. Most people serious on mythology are quite used to really modern writing. Anything about Egypt, Akkad, Sumer, written before 1970 is obsolete. All my main grammars in those languages are past 2000. Any person loving mythology should not reject modern "authors" without a good reason to.